Multi-pole low voltage circuit breaker with one current measuring device per line

ABSTRACT

A current measuring device ( 15 ) for a multi-pole low voltage circuit breaker ( 1 ). comprises a support body ( 20 ) with a through opening for a current conductor ( 4 ) for each of the poles and a receiving chamber ( 22 ), surrounding the through opening ( 21 ), for secondary components ( 26, 31 ) of current sensors and/or current transformers. The support body ( 20 ) is essentially plate-like and rectangular and forms part of the rear wall ( 13 ) of the circuit breaker ( 1 ). Should Rogowski coils ( 26 ) be used as secondary components of a transformer, then adjustable voltage dividers are also mounted on the support body for interdependent adjustment. The multi-pole current measuring device ( 15 ) simplifies the production of circuit breakers as approved components.

[0001] The invention relates to a multipole low-voltage circuit breakerhaving an enclosure and having one current detection device for eachpole, with each current detection device having an electrical conductor,which is associated with a switching contact system for that pole, and asecondary part through which the electrical conductor passes.

[0002] Circuit breakers of the stated type have been disclosed, forexample, in U.S. Pat. No. 4,673,779 or U.S. Pat. No. 347,623 (DesignPatent) in conjunction with U.S. Pat. No. 4,497,992. The currentdetection devices provided there have the object of producing a signalwhich is dependent on the current flowing in each of the poles and whichis evaluated in an overcurrent tripping device, in order to interrupt acircuit for protection of loads and electrical systems. Since, in somecircumstances, only one of the poles of a circuit breaker may beaffected by a high fault current, each of the poles is equipped with acurrent detection device.

[0003] The secondary parts of the current detection devices generallycomprise a mount and a winding which is fit to it and which may be asingle-layer winding or a multilayer winding. Furthermore, thesecomponents are generally provided with an enclosure or a casing forprotection against damage and against external influences. During theprocess of manufacturing a low-voltage circuit breaker, the secondaryparts of the current detection devices are selected and mountedindividually in accordance with the user's requirements. Suitablerecesses or pockets are provided for this purpose on the rear face ofthe enclosure of the circuit breakers, through which the electricalconductors which are connected, to the switching contact systems extend,and at the same time form connecting means for connection to a circuitthat is to be protected. Once the secondary parts have been pushed ontothe electrical conductors, suitable sealing covers are fit to the rearface of the enclosure, in order firstly to protect the secondary partsof the current detection devices, and in order secondly to support theelectrical conductors on the enclosure of the circuit breaker, as closeas possible to their connection point. The reason for this measure isthat circuit breakers of the type mentioned are subject toextraordinarily high mechanical forces in the event of a short circuit,which can lead to damage to the circuit breaker and to the conductorscontinuing on from them if busbars are not adequately supported.

[0004] The invention is based on the object of improving the currentdetection in multipole low-voltage circuit breakers, and of simplifyingthe installation of the current detection devices.

[0005] According to the invention, this object is achieved in that thesecondary parts of the current detection devices for all the poles ofthe circuit breaker are arranged in a common mounting body, which hasaperture openings for the electrical conductors as well as attachmentmeans for detachable connection of the mounting body to the enclosure ofthe circuit breaker.

[0006] The combination, as envisaged according to the invention, of thesecondary parts of the current detection devices of all the poles toform a standard assembly makes it possible to provide units, which arematched to one another and are tested together, for current detection inmultipole circuit breakers. This reduces the time required formechanical installation and calibration and adjustment of the completedcircuit breaker. The multipole mounting body at the same time improvesthe mechanical strength, by supporting the electrical conductors in acohesive body.

[0007] The mounting body which is provided according to the inventionmay have recesses for holding the secondary parts, with these secondaryparts being mounted in the recesses by encapsulating them with asynthetic resin compound. It is thus possible to use the same materialsand production methods not only for production of the mounting body butalso for the attachment of the secondary parts, as those which arealready known for the production of the enclosures and of enclosureparts of circuit breakers, and of the associated single-pole currentdetection devices.

[0008] For the purpose of the invention, the mounting body, whichessentially has a rectangular outline and is in the form of a panel maybe configured as part of a rear wall of the enclosure of the circuitbreaker, with the recesses which have been mentioned being arranged onthat side of the mounting body which faces the interior of the circuitbreaker. This arrangement provides good protection for the secondaryparts against damage during handling of the circuit breaker and has agood protective effect on the electrical conductors which are associatedwith the current detection devices.

[0009] As already mentioned, the current detection devices forlow-voltage circuit breakers may be of widely differing types. Onefrequently used type is the transposed conductor current transformer,which has a nonmagnetic mount surrounding the electrical conductor andhas a single-layer winding, whose start and end are directly adjacent toone another. The output variable from a current sensor such as this is,in contrast to inductive current transformers, dependent not only on thenumber of turns, but also on their geometrical distribution andarrangement. According to one refinement of the invention, in thiscontext, it is possible to compensate for the different transmissionresponse of the transposed conductor current transformer resulting frommanufacturing tolerances by each of the transposed conductor currenttransformers having an associated voltage divider, which is composed ofresistors, and by these voltage dividers likewise being fit to themounting body. The adjustment of the transposed conductor currenttransformers can therefore be carried out before they are installed in acircuit breaker, which represents a simplification in comparison to thepreviously required matching and calibration of the completed circuitbreaker.

[0010] The voltage dividers which have been mentioned may each beconfigured such that they can be adjusted by means of an adjustmentelement, with all the adjustment elements being arranged in anaccessible manner on the rearward face of the mounting body. The currenttransformers and current sensors can thus be adjusted convenientlyduring the production process. However, in order to ensure that theadjustment which has been carried out is maintained in allcircumstances, it is recommended that it be possible to protect theadjustment elements against inadvertent operation by means of an accessbarrier, which can be fit once the adjustment process has been carriedout. In this case, an encapsulation compound which covers each of theadjustment elements is particularly suitable for use as the accessbarrier.

[0011] As already mentioned, the current detection devices in alow-voltage circuit breaker provide output variables which are processedin a tripping device. The auxiliary energy which is required foroperation of such a tripping device is generally likewise obtained fromthe electrical conductors of the circuit breaker by means of a currenttransformer. In this case, it has frequently been found to be expedientto provide a separate current transformer, which is independent of thedescribed current detection devices, in order to provide the auxiliaryenergy. In this context, it is already known for a current sensor whichis provided only for measurement purposes, and for an inductive currenttransformer, which is used to provide auxiliary energy, to be arrangedin a common enclosure. For the purposes of the invention, this method ofconstruction can also be used in a multipole mounting body, in such away that a least one separate current transformer, which is used forsupplying power, is arranged on the common mounting body.

[0012] The invention will be explained in more detail in the followingtext with reference to the exemplary embodiment which is illustrated inthe figures.

[0013]FIG. 1 shows a multipole low-voltage circuit breaker schematicallyand in the form of a section.

[0014]FIG. 2 shows a mounting body, which is intended for a three-polecircuit breaker, for current detection devices, with a view of theinside facing the interior of the circuit breaker, while the mountingbody is shown from its outside in FIG. 3, and is shown in profile inFIG. 4.

[0015]FIG. 5 shows a sensor coil, without an iron core, for a transposedconductor current transformer, while FIG. 6 shows the secondary part ofan auxiliary current transformer, as individual parts of a currentdetection device.

[0016] The three-pole mounting body which has already been illustratedin FIGS. 2, 3 and 4 is shown in the form of a perspective illustrationin FIG. 7, showing the secondary parts of a current sensors andauxiliary current transformers arranged in holding chambers in themounting body.

[0017]FIGS. 8 and 9 show details of one embodiment of a currentdetection device, with adjustment elements and an access barrier forthese adjustment elements.

[0018] The low-voltage circuit breaker 1 which is shown schematically inFIG. 1 has an enclosure 2, on whose rear wall 13 busbars 3 and 4project, for connection to an external circuit. The busbars 3 and 4 arepart of a switching contact system 5 which has a stationary switchingcontact 6 as well as a movable switching contact 7. An arc-quenchingchamber 10, for quenching switching arcs that occur when the switchingcontacts 6 and 7 are open, is located above the switching contact system5. The movable switching contact 7 is fit to a movable contact mount 11,which can be operated for opening and closing by means of a driveapparatus 12. The electrical conductors 3 and 4 are connected directlyto the switching contact arrangement 5 and are supported on a rear wall13 of the enclosure 2 with respect to all the forces that occur. Theopening of the switching contact arrangement 7 in the event of a faultis controlled by a tripping device 14, which is indicated above thedrive apparatus 12. For this purpose, the tripping device 14 receivessignals from a current detection device 15 whose primary part includesthe lower electrical conductor 4, which is surrounded by a secondarypart 16 of a current sensor. This may, in a known manner, be aninductive current transformer, a current transformer without an ironcore based on a transposed conductor coil, as well as the sensors whichact on the basis of other known principles. For the present purposes,the components of a current detection device also include auxiliarycurrent transformers which are provided, in a known manner, forsupplying the operating power or auxiliary power to the electronictripping device 14.

[0019]FIGS. 2, 3 and 4 show how the secondary parts 16 are arranged andaccommodated in a three-pole version of the circuit breaker 1. Theessential feature for the arrangement of the secondary parts 16according to the invention is a mounting body 20 which is common to allthe poles that there are in the circuit breaker 1 and may be composed ofa molded material, such as that which is also used to produce enclosureparts for the circuit breaker 1. The mounting body 20 has a suitablerectangular aperture opening 21 for the upper electrical conductors 3 ofeach pole of the circuit breaker 1. As can be seen in particular in FIG.3, this aperture opening 21 lies in the plane of the rear wall 13 of theenclosure 2 of the circuit breaker 1, so that the support for thebusbars 3 is removed as far as possible from the stationary switchingcontact 6, thus resulting in a good supporting effect. Each of theaperture openings 21 is surrounded by a holding chamber 22, which isused to hold the secondary parts 16 of the current detection devices 15.As already mentioned, current transformers may also be accommodated inthe holding chambers 22, and are used to supply power to the trippingdevice 14.

[0020] For attachment to the rear face of the circuit breaker 1, themounting body 20 has on its lower longitudinal edge a web 23, with acorresponding groove being provided on the rear wall 13 of the circuitbreaker 1 in order to hold this web 23. Recesses 24 on the edges andaperture openings 25 between the poles on the longitudinal edge of themounting body 20 opposite the web 23 are provided for attachment means,in particular for screws which engage in the enclosure 2. In conjunctionwith the web 23, this results in the mounting body 20 being heldsecurely on the rear wall 13 of the enclosure 2 (FIG. 1).

[0021] As an example of a current sensor, FIG. 5 shows a transposedconductor coil 26 with connecting lines 27 indicated, which correspondsto the secondary part 16 in FIG. 1. A coil such as this supplies asignal which can be evaluated electronically, in order to control thetripping device 14 which has been mentioned. This requires auxiliarypower in order to make it possible to carry out the necessary evaluationand calculation processes and, when necessary, to operate a trippingmagnet. A separate auxiliary current transformer with a secondary part31 is provided, as shown in FIG. 6, in order to provide this auxiliarypower, and its primary winding is formed by the associated electricalconductor 4 of the circuit breaker 1 (FIG. 1), as in the case of thetransposed conductor coil 26. The secondary part 31 which is shown inFIG. 6 has an iron core 32 and a secondary winding 33 seated on it. Anelectrical conductor which is used for the primary winding is indicatedby dashed-dotted lines, for simplicity, in FIGS. 5 and 6.

[0022]FIG. 7 shows how the secondary parts as shown in FIGS. 5 and 6 areaccommodated in the holding chambers 22 of the mounting body 20. Theright-hand one of the holding chambers 22 will be considered first ofall. As can be seen, the holding chamber 22 has a hollow-cylindricalexterior and is matched to the diameter of the transposed conductor coil26. The inner boundary of the holding chamber is formed by a collar 34,which surrounds the aperture opening 21.

[0023] The left-hand part of FIG. 7 shows a state which occurs duringthe manufacture of a current detection device 15, in which a transposedconductor coil 26 and a secondary part 31 of an auxiliary currenttransformer are introduced into a holding chamber 22. The transposedconductor coil 26 in this case touches the bottom of the holding chamber22, and is aligned on its hollow-cylindrical circumferential surface.The secondary part 31 of the auxiliary current transformer, which isseated on the collar 34, is located above this.

[0024] Although it would be possible to mount the coil arrangements inthe holding chambers 22 by means of a cover which can be connected tothe mounting body 20, encapsulation with a synthetic resin compound ispreferred. This encloses the coils and connecting lines on the secondaryparts, and thus provides good protection against all externalinfluences. Such encapsulation with a synthetic resin compound 35 isillustrated in the central part of FIG. 7.

[0025]FIG. 7 also shows that a lower region 36 of the mounting body 20is configured in a closed manner between the central holding chamber andthe right-hand holding chamber 22. The adjustment elements 30 (FIG. 3)for the voltage dividers which are associated with the current sensorsand the transposed conductor coils 26 are located in this area. Theseadjustment elements 30 need be adjusted only once, once the currentdetection device 15 has been completed. In order to avoid randomoperation subsequently, an access barrier 37 may be provided, as shownin FIGS. 8 and 9. This is a cover which is attached by means of a screwthat is prevented from rotating by means of a tab 38.

[0026] The combination of the secondary parts of the current sensors andauxiliary current transformers of all the poles of a circuit breakerresults in an assembly which is ready for installation and iselectrically adjusted. The calibration of the secondary parts, and acomplete test of a multipole current detection device, may be carriedout before installation in the circuit breaker, which represents aconsiderable simplification. This reliably avoids faults, for example asa result of confusion between previously selected secondary parts thathave been provided. This also ensures that all the secondary parts arearranged at a defined distance from one another, which cannot be varied,and that subsequent faults and tolerance problems are precluded.

1. A multipole low-voltage circuit breaker (1) having an enclosure andhaving one current detection device (15) for each pole, with eachcurrent detection device having an electrical conductor (4), which isassociated with a switching contact system (5) for that pole, as aprimary part and having a secondary part (26, 31) through which theelectrical conductor (4) passes, characterized in that the secondaryparts (26, 31) of the current detection devices (15) for all the polesof the circuit breaker (1) are arranged in a common mounting body (20),which has aperture openings (21) for the electrical conductors (4) aswell as attachment elements for detachable connection of the mountingbody (20) to the enclosure (2) of the circuit breaker (1).
 2. Thelow-voltage circuit breaker as claimed in claim 1, characterized in thatthe mounting body (20) has holding chambers (22) for holding thesecondary parts (26, 31), and in that the secondary parts (26, 31) aremounted in the recesses (22) by encapsulating them with a syntheticresin compound (35).
 3. A low-voltage circuit breaker as claimed inclaim 2, characterized in that the mounting body (20) which essentiallyhas a rectangular outline and is in the form of a panel is configured aspart of a rear wall (13) of the enclosure (2) of the circuit breaker(1), and in that the holding chambers (22) are arranged on that side ofthe mounting body (20) which faces the interior of the circuit breaker(1).
 4. The low-voltage circuit breaker as claimed in one of claims 1 to3, characterized in that when using transposed conductor coils (26),each of these coils has an associated voltage divider, which is composedof resistors, and in that the voltage dividers are likewise fit to themounting body (20).
 5. The low-voltage circuit breaker as claimed inclaim 4, characterized in that each voltage divider is configured suchthat it can be adjusted by means of an adjustment element (30), and inthat all the adjustment elements (30) are arranged in an accessiblemanner on the externally accessible side of the mounting body (20). 6.The low-voltage circuit breaker as claimed in claim 5, characterized inthat the adjustment elements (30) can be protected against inadvertentoperation by means of an access barrier (37) which can be fit once theadjustment process has been carried out.
 7. The low-voltage circuitbreaker as claimed in claim 6, characterized in that the access barrieris formed by an encapsulation compound which covers each of theadjustment elements (30).
 8. The low-voltage circuit breaker as claimedin one of the preceding claims, characterized in that at least oneseparate current transformer (31), which is used for supplying power toa tripping device (14) for the circuit breaker, is arranged on thecommon mounting body (20).